1. Technical Field
The invention relates to a polarization control element, which uses polarization anisotropy created by a structure shorter than a wavelength of light to be used (hereinafter referred to as the “sub-wavelength structure”).
2. Related Art
In recent years, a polarization control element constituted by inorganic materials is attracting attention. Such polarization control element has higher light resistance and heat resistance than the polarization control element of a currently available type using organic materials. Much expectation is entertained for its application to a variety of optical equipment that utilizes polarization.
There have been made several proposals on the polarization control element made up of the sub-wavelength structure. For example, in the U.S. Pat. No. 6,122,103 specification (a first example of related art) and the U.S. Pat. No. 6,244,3199 specification (a second example of related art), it is disclosed to the effect that a periodic metal grid pattern (striped structure) formed on a transparent substrate such as a glass substrate functions as the polarization control element. Further, it is mentioned in these documents to the effect that as metallic materials to form the metallic grid pattern, aluminum and silver may be employed.
However, in each of the above-referenced documents, guidelines not only for selecting a metallic material to form for the metallic grid pattern but also for engineering its optical constant are not disclosed. Since selection of the material and design of the optical constant are determined on a trial and error basis, through trial and error, it is unknown whether aluminum and silver illustrated in each of the documents is truly the best choice or not.
As a result, it is desired to develop a method (or methodology) which makes it possible to provide guidelines as to which material having what properties should be selected or how new material development should proceed, if a polarization control element having better properties by making effective use of a high potential of the sub-wavelength structure is to be realized.
The U.S. Pat. No. 6,122,103 specification is a first example of related art. The U.S. Pat. No. 6,243,199 specification is a second example of related art.